Means for ringing over multiplex transmission channels



May 8, 1923- 1,454,159

L. ESPENSCHIED MEANS FOR RINGING OVER MULTIPLEX TRANSMISSION CHANNELS Filed July 301-. 1920 2 Sheets-Sheet 1 Q q 7 k v 7 IINVENTOR llgygllglzmmzkd ATTORNEY May 8, 1923- 1.. ESPENS CHI'ED mums F o'R RINGING ovsa uumxrmsx TRANSMISSION cumu us Y Filed July 50-, .1920 v zisneets-sneet 2 luvzmga ATTORNEY Patented May a, 1923.

" (UNITED STATES orr cE.

' LLOYD i-zsrmiscmsn, or QUEENS, mrw roux, .tssmnoa 'ro annnrcnn 'mnnrnoma" am) rnnnonarnpoiurmr, a coaroaa'nou or NjawYonm arms mt nmsmo oven mun'rlrnnx 'rnausmss'roircrrimmnsx.

314,074, filed Jul e's, 1919.

.Wliefe multiplex, transmission is attained by tap-use of carrier currents a pluralityof carrier frequencies are transmitted over a common transmission line, the. carrier fre quencies being separated sutliciently to,pre vent interference, and each frequency-be:- ing assigned for use. as aseparate channel of communication so that signals, such, for instance as telephonic variations, may be transmitted by unpressin'gthem upon the carrier frequencies. I Several channels-may thus be superposed upon'a common trans-,

mission line andeach channel performsthe functions of an ordinary telephone transmission line. 9

In ordinary telephone transmission it is customary to transmit over the line, in atldition to the telephone currents, ringing currents or other signaling currents. for the punose of signaling between operators in est: lishing connections. In order to ob- ..tain practicaltelephone service over each carrier communication channel. it isdesirable that the channel be, utilized forthe transmission of such ringing or other sinnaling currents as well as for the transmission of ordinary'telephone currents.- This invention. therefore, concerns ineans whereby ringing and other signals may be transmitted for 'each carrier channel. ihe im-ention likewise has reference to the provision of a transmissionsystem having included therein a vacuum tube which normally acts to produce one desired result, hutwhich under other'comlitimis operates as a generator of oscillations. A further feature of the invention is the provision in a transmission circuit of an amplifier, which, while normally serving as "a e -1 nece ai- 1920, s mi-memes;

an amplifier only, will under certain conditionsroperate toproduce oscillations.

Still anothernpart of'the invention relzites to an amplifier between two line see tions for the amplificationof current-transmitterl from one line-section to thevother,

which in response 'to icurrents transmitted from'saidlast mentioned 1ine s'ection, will .act as a-generatoro'f o scillationsto be transmitted tofthe;.first 'line section.

- The :aboveffetures, as well as others more fully"hereinaftenappear nfi,-are? n' 'plified diagram of -sachl-.por nons;-of the apparatus'g and lcircuits ofa 'carrier system as 'for-a full understanding of the inventiom and Figure 2.,ofwhichillustrates the invention :as applietl to an ordinalrzy22repeater system.

eferring to Fig. .1: of the drawing,s ML designates a mam line cmployedinfer the terniinalf-carrier equipment is provided for separating the frequencies-intoqtheir respective channels and 'for associating them with loan-frequency transmission line A portion ofthe apparatus at one 'station only is illustrated, it being'understood that simi- "lar apparatus will be providedpat; thetother station, At thestat-ion illu'stratedin the drawing.the main line ML is'balanced by an artificial line MN! and is associated through a halancedjtransformer arrangement IO'with a.- common transmittin cirvcuit TL and a. common receiving circuit RL.

- the other.

The common transmitting,' and receiving k n-mas .TL and RL are associated with a terminal low l 're('1uency line I), through a two-wav circuit comprising a transmitting channel TL, and a receiving channel RL,,'

transmission ci a-plurality of ;carrier fre- -quenc1esbet een two' main stationsatavhich the former channel being inductively associiit'ml with the common circuit TL through a connection including. filter TF, and the latter channel being inductivelyassociated with the common receiving circuit BL through a connection including 3.

filter RF, The transmittingand receiving channels'TL and RL, are interconnected at their ends through a transformer arrangcment. 11 with tlie terminal line L the latter line being balanced by an artificial line or network N so that the transmitting and receiving channels TD and RH will be conjugate with respect to each other. The common transniittingv'andreceiving circuits TL and RL, may be similarly associated with one 'or more other low'tre-- quency terminal lines through transmitting and receiving channels similar to TL and 'RL the manner in which additional channels are associated with the common circuits TL and BL being indicated by the connecband filters of the general type illifiltrated tions including the filters TF v and RF The transinittin channel TL a includes,

in addition to the filter TF a similar filter These filters rare preferablyjbroad in U. S. patents issued to George A. Campbell, Nos. 1,227,113 and 1,227,114; dated May 22, 191". These filters. should be so designed as to "transmit a band of frequen ciesequal in width tothe band of frequncies employed in ordinary telephonic transmission, said band extending from the carrier frequencyassigned' to -the channel to a limiting frequency either above-or below said carrier frequencyan amount equal to the width of-the band.-

In order to translate the low frequency" signaling currents transmitted over the line [L into high frequency currents for transmission over the main line .ML. the transinitting clianncl TL, is provided with a trated-aiid described in the l tionot l5. Kendall. Serial No. 123,349,- filed October 13. 1916. or in the-l S. pat ent to John R; Carson;No.1.34fii307. issued modulator M This modulator isp'ret'erably of the duplex vacuumtiibejtype illus- Sl applica- June [5, 1920. 'lhe modulator M, is supplied with carrier oscillations of the t re quency' assigned to the channel over a circuit 12, but as these oscillations are impressed on the common conductor of the bal- 'pull type.

,"TliQ receiving channel RL includes. in addition to the filter RF a filterlilfl') These filters are likewise of th" general type illustrated and .described in the patents'to (amphell above referred to. the filtcr'RF being similar in structure and transmitting a band of frequencies similar to thattrans mitted by the filters TF and TF,'. The filter R1 however, is a low frequency filter designed to transmit a range of frequencies extending from zero up to the up- -per limitingfrequency employed inordinary telephonic transmission.

The receiving channel RL, also includes "a demodulator or detector D,. This detector may be 0tv any well know type but is illustrated as being of the duplex vacuum tube type, illustrated and described in the U. S. patent to John R. Carson, 'No. 1,343,308, issued June 15, 1920, As set forth ,in the said patent to John .R Carson', this demodulator operates in accordance with the so-called homodyne method of receiving and is, therefore, supplied with oscillations of the same frequencyasvthe corresponding modulator. Tlieseoscillations are supplied over the circuit 13 to -the common branch of the balanced input circuit of the demodulator so that normally. noihigh ire uency oscillations are transmitted throu'gi the demodulator. v

The receiving' channel BL," is also provided with an}aInplifiei-FRA for tli'epurpose of. amplifying-the. detected -;low frequency currents. This amplifier may be "of any well known type; butgfas l l; i llustrated is a vacuum tube 'haring 'its; input"circuit 'conpledrwitlr its output circuit through a concoupled tlirough ii tra-nsfo'riner 15 with-a circuitincluding conductors 16, 17 and.18,

conductors 1 6 andIS lieingr nnected, to one wind ng of a transformer 19 in'the' output circuit of the amplifier. Conductor 17- is normally connected inserics witlrconductor 18 and includes 'a' condenser 20. 'while the conductor 16 includes an inductance 21 A coiidenser 22 is bridged across the primary w ndings of the transformer 15, thereby queneyl In the ain 'i'liticatioii ot' telephonic currents which may he eonsidci'edto extend doi'niing a gairciiitiresonant at a critical freoreia range from' about 300 cycles-to about 2.001) cycles. the feedback connection-chore described is'without substantial ellect ..andthe amplifier operates to amplifytelephonie.

frequencies 'iii'tlie ordinary manner. It. is desirable, however. that the deteet'edringing currents whichjwill lzeimpressed upon the amplifierfasherei naftcr described, shall be amplified 'to' a greater degree than the tails,

i'iig currents. These ringing currents should heofsouie trequency outside the telephone range describedfais, for instance, 133cycles.

liy means of'the condenser 22, the circuit- 14 is therefore tuned to resonate at 133 cycles. The pi ii'nary oftlie feed back coil 15 is di- \ided into two parts similar but reversed in respect, to their subsequent circuits. The phase relations established by one of "these circuits, that "associated with condenser 20,

currents of other frequencies from other channels are impressed upon the circuit TL. 1 The several-modulated frequencies are trans mitted through the transformer and over the main line ML to the distant station.

Carrier currents haying frequencies corstation of Fig. 1 and modulated at the dis-' tantestation in accordance with telephone i signals,- after being transmitted over the line ML, pass into the common receiving circuit RI). from which the different carrier frequencies are selected into the proper receiv ing channels through the agenc' of-filters such' as RE. RF. etc. The mor ulated -car-' rier oscillations passedthrough' the filter oscillations were. modulated at the istant stated, is so arranged as to cause the am 1i;

station. 1 The low'frequency telephonefcur-f' rents thus supplied are impressed u n the -amplifier RA, andaretransmitte d t rough the amplifier without substantially.afl'ecting w the feed back circuit, which," "as already,

fier to reamplity oscillations having a re quency of 133 cycles which is'below the; lower limit of telephone currents.

telephone currents are therefore amplified" by the amplifier RA 'in the' norm'al manner and are transmitted through the; trans "former 19 passing through the low ire:

, designed to be affected with 'quenc ,filterRF, to the midpoints of-the trans ormer 11. The bridges including the relay" 23 and the anti-resonant combination 26-27 do not materially decrease the trans' regard to cur-' rents in the neighborhood of 133 cycles only. The telephone currents upon arriving at the midpoints of the' windings oi. the transformer 11 divide,- part of the energy flowing to the artificial line N, and {fart of t-heen; ergy flowing over the back contacts' of the relay 29 to the line-L Ringing current transmitted over the line L, from a' distant terminal statlon passes over the back contacts of the relay -29and through the windings of the ringing resonsive relay 31.. Condensers 3'? and..38,havmg a high impedance to "rmgmg currents, but readily permitting. the ymssage of telephone currents, may be inserted between the relay 31 and thetransform'er 11 to insure that the greater proportion of the energy i li -fi i i 99 8 .jr'ight hand front opens the; bridge in of the ringing current transmitted. from the line L shall be impressed upon the relay 31.

at itsleft-hand contact disconnects ground from the normally opened circuit of the relay. 29 to prevent any possibility of this re lay being actuated to connectringing -eur- Relay 31,.in response to the rin ing current, opens a circuit of the slow actlng relay 32, which completescircuits energizing relays 33 and 36. Relay 33, upon being energized,

rent "from-a local sou'rce-tojthe line L H-"At responding to the several channels at the its front left-hand contact relay 33 -connects firoundfdireetly to the grid of the amplifier potentiometer 39; At its right-hand; front contact, relay L36 disconnects-conductor "18 that the feed back circuit is so adjusted that" the'amplifier. oscillates at 133}cycles to I from conductbr. 17 and connects it to c'ondnctor 3t which includes the condenser 35,*so,

generate' ringing current. "A distinct adyantage arisesfrom the short circuitingof" the time, under practical opefatin'gxconditioiie to y h ema fieet e i e' mllifis RA, in; accordancetwlth" thehtr cuiti'ng? the potentiometer; tithe; 'plifie when; functioning a'e"zan .='oscillator in theamphtude ingiener cludiii the-relay 23, there y preventing sai aw min being actuated;wake-183"' ea oscillatiof s l supplied by the. implifier" A,

and .at the' 'same timeiit'short circuits the anti resoiiant combination 126- 27, .which if it' remained. in the circuit,-,would ub stantially prevent; the transmission of the '-oa-" cillations toth'e transformer 11. Atitsi-left hand front contactrelay '36 connects-a short otentiometer 39 in the. .manne1 r ;just deserl 'd, due gtogthefact that-the setting of the potentiometeryisy varied from? time p ission conditions ofthe circuit, and'by shortcirmme e epems will aim 1 circuitacrosstlieleithand terminalsof the mission of=the channel RL,, since they are line windings ofthe transformerll, thereby unbalancing the circuit sothat transmissions, i maytakeplacefromlthe receivmg channel I RL' through the transformer 11 to the transmitting cl1annel,TL,. The 133 cycle oscillations are now transmltted item the. am.-

through the transfo 11 to the. input circuit'of'the moduhitor I,. The 133 cycle'oscillations thus trahsm tted operate to modu late the carrierfrequenclsyl t r t filter TF common circuit TL, transformer manner'as described inconnectioii'fi'vith tele andOYer the main line ML to the distant station.

In case it is desired to ringover the line i "L,- from the distant station, the carrierapif'pu'atus at that stationwill be operated in circuit of the demodulator D' These modulated. oscillations reset in the demoduliitor D,- withunmodulated oscilletions from the, circuit 13 to-produce in the output, circuit of the demodulator 133 cycle ringing our 7 rents, which are then impressed upon the I 'relixy 23'.- Relay 23 upon" being' energ'ized ures "olp'ens the circuit of the slow i .t e

a manner similar to'that just described so that carrier oscillations modulated in air cordence with 133 cycle ringing current will be transmitted over the main line ML and into the common receiving circuit RL. The I carrier oscillations are'then selectively trainsmltted through thefilter RF to the input amplifier RA This amplifier having its feedback circuit in its no'rmalcoiiditionacts as a. reamplifier at a frequency of 133 cycles and consequently the ringing currentsare amplified to a much greater. egree than-in the caseof telephone currents. The highly amplified ringing currents ere then pessled through the filter RF ani'f flow through the bridge, including thg' N15? 23 tbfqp iete said relay, -tlie ji,enti -resonent combination, '2627 at; the iime time""functioning h vent any substential vgnnount ofiltl e fr energy from 'being trgnsrnittedfibey .ec i

reby 'completin the c rcuit o I reluy'i29, {which at its outer ontcontuctsfdisconnects ithe line-L from the transformer-" 11 end-ap T plies =0. local source of "ringinggcurrentf to 'saidline. At its inner" fronteonteetsf layI 29-et'the same time substitutesien iiuxi iery' line 30,for the line L so that the balan'ce'of V v the-transmittingend' receiving chdnnelsi'I-I and RL', is maintained;

, an ordinary 22 ripeeter circuit. In fig-." designate two'lo'iv; fre

i--Fig;2 illustrates the use of a device ivhich normallyfunctions as an amplifier as I a source of ringing current for-ririgihgthrough ure, LE and L quency transmission lines balanced by artifi amplifier AE and a, receiving'channel' RW,

cia-l lines or networks NE;and NW respectively. Amplifiers AE and, ;UV are shown,

these amplifiersbjeing, as illustrated, of thewell known vacuum tube type, although the inventiori' is equally applicahle'toother well .known t channel. -W leads from thelirie LW to the leads from theamplifier. AW to the line LE.

being inductively zissociated' therewith through the transformer -11. The transmitting channelTE connects the line'LE to the amplifier. AlV while the receiving channel leads from the'amplifier Al) to the line LE, being inductively associated lhercvvith through the transformer 11'. The em'plifiers AE-and A W normally funcs of amplifiers. A transmitting quency in a well known manner. hutthey. are so arranged that the input and out mt circuits may be coupled together so that the tubes oscillate at some suitable ringing frequency, as, for example, 133 cycles second The coupling ofithe input and output circuits of tion to amplify currents of telephonic frethe ainplifier'All Ls controlled through suitvuble'relay iirrengcments, the action of which is detern'lincdihy a ringing responsive 're layefl, brid ed across the transmitting channel'-TW '%he ringing responsive relay 40 also funeti ons'. to provide a path whereby the rin 'in current generated by the inn lifi er A15 may be transmitted to the line E.-

In a similar manneiy a ringing responsive relay 41; bridged acrossthe transmitting channel TE, controls throu h -a suitable chain of relays the coupling of the input and output circuits of theum lifier AW to transmit-r ngingieurrent. tot e line LW.

'Fnrtlierlfdetailsjof Ville 'epparatus wm be clear from a description of its,operation, whichjsfisffolloivsz Tele lionecurrlentstohe'transmitted from ugh the transformer 42 end :pumugmtdle ]to the iimplifier AE.

' Lfamplified .telephone currents appearing hefoutput circuits of s e P rough;the'ftrens'forine windh'. the transformriinsform'er' 47 andlp'oten io etc Thfiiiniili 'ed' currents 'are tliei transmitted through "the transformer comprising wind over the meme] contacts of i'n'gs 49;:i'nd 0 he'circuitRW from which 'hir c' uitsthey Ringing curreht incoming over the'line "LWpa'sses-over the normal contactso'f the the windings" of the ringing responsive re- .lay'40.' The ringing responsive relay 40 causes the release of the slow acting relay 53, which closes the circ'uit'lthrough relays 46 and 54;Relay 46, upon being energized,

'shifts'the' connection from. the win ding 45 of the outputkn nsfonner of the amplifier A'E fi-om theiiigodit RE to thecircut 55. The lower armetui 'e'of the relay 46 at the same time disconnects the grid of the amplil ne'iLEfpess'to the (:ir-

trensmittedkthrough the gtmnsformer llito the line LW. 3 p

fiei' Alf)fro'mthepotentiointer 43 and con nects said'grid to an'oscillating circuit including a Winding 56 and a-condenser 57. .The' winding 56 is in inductiverelation with;

'the windings 4! and 45,-andthe output and input circuits ofthe amplifier AE are now coupled together so that the amphfier acts as'a generator of oscillations, the frequenely of which is determined by the oscillating circuit; The oscillating circuit is so tuned that the frequency generated will be a frequencysuit'able'forringing, such for example, as 133 cycles. The ringingcurrent thus enerated is transmitted to the circuit 1 55. he relay 54, which was energized at comin the same'tinie as relay'46, disconnects the.

line LE fromthe transformer 11f and directly connects said line to the circuit 55 so that the ringing current istransmitted over the line LE. c

In a similar manner, ringing current 'inl over the line LE passes over;the norma contacts of the relay 5 k to the circuit TE, actuating the ringing responsive relay 41. The rela 41 opens the circuit of the slow acting re ay 58 which in turn closes the circuit of relays- 51 and 52; Relay 51,- upon the amplifier AVV from the circuitRIV and being actuated, disconnects the winding 50 of the transformer in the output circuit of connects said winding to the'cir'cuit'59;' f-At the sameti'me, the lowen armature of the relay 57 disconnects the grid of the ampl fier AW from the potentiometer 48 Iand connects said grid to an oscillatingcircuitineluding a wind'ing 60,, and a condenser-61. The winding is inductively related to the windings 49 and 50 so that the input and,

output circuits of the amplifier are now cou- 'pled together and the amplifier oscillates; at

" a frequency determined by its oscillation circuit; This frequency is set at the desired ringing frequency, which in the case under consideration, may be 133 cycles per second.- This ringing. frequenc is transmitted over the front contacts of t 1e relay 51 to the circuit 59." Relay 52,,aponbeing energized," disconnectsline LW from the transformer It and connects said line tothe circuit 59 so that the ringing current generated by the amplifier 'AVV is transmitted to the .line L'W.

It will be seen that by means of the arrangements above described a simple and yet efficient circuit has been providedzwhereby ringing signals may be transmitted over the same channel of a multiplex system as is used for telephonic transmissions-It 'will also be seen that in accordance .with this-invention, a vacuum tube is provided, which, while normally functioning to produce one result, may be, under certain circumstances, caused to function as a generator of ringing 'current, and while in the system as herein disclosed, it has seemed most convenientmo employi 'thc vacuum. tube which normally functions as an amplifier for this purpose,

any other vacuum tul-- in the system might equally well he used for the same purpose. It will likewise be obvious that while the iu\'ention has been illustrated as embodied in certain apparatus which has been found to be desirable from-a" practical standpoint,

be em rent transmitted from one; of said tions to convert said amplifier into a genthe gepgrgl principles herein disclosed may [transmitted from'one section to the other,

and means responsive to currents incoming from thelatter' section to cause said'amplifier to function as-a'nl independent source section.-

3. In asignaling'system-Jwo transmission of oscillations fortransinission to the former line sections; an lifier" interconnecting ed in many other organizations:

said sections .for amp 'iyingringingcurrents 3 transmitted from one section to the other,

and meansresponsivelto ringing currents incoming-1mm .tlfis, latter section to cause said amplifier to function as agenerator of winging. gcunent .for- "transmission to the former section's. I

4. In a-signaling system,qtwo'transmission l-inmeections, a tw'oway circuit. interconnecting said. sections, "said, two-way circ uit comprising 3 two 2 paths M for transmission in pipositej directions, an amplifier in one of sax .pa-ths,'-means toconvert said am, plifier. into a. generator of oscillations at will, and means to transmit the oscillations so generated .to one ofsaid line sedions.

5. In a signaling system, two transmission line sections, a'twoway circuit interconnecting said sections, saidtwo -way circuit comprising two paths for transmission in oppositef-directiongan. amplifier in one of said paths,- and'me'ans respondin to ourerator of "oscillations;

6. In a signaling system, two transmission line sections, a'two-way circuit interconnecting said sections, said two-way circuit comprising two .paths' for transmission invopp osite directions,, an'amplifier in one of said paths, andmeansresponding boringing' current transmitted. from one of said line sections to convert said amplifier into a generator of ringing current;

path, a vacuum t'ube'and circuits therefor normally functioning with respect to said path to translate currents transmitted'over said path,and means whereby the input and output circuits of said tube may be coupled together at will under the control of said 7. In a signaling system, i!. transmission path so that said tube becomes a, generator ofoseillations. e

8. In a. signaling system, a transmission path, a vacuum tube and oircuitstherefor 5 normally functioning with respect to said path to translate currents transmitted over July 1920. said path, and means whereby the eircuits j IJOYD ES ENSCHI D. 

